for example the good old pacman runs at 60.61 Hz.
So if you run it on exact 60.00Hz, you are running with ~98,99%.
So this makes pacman about 1,01% slower (and the sound pitch those 1% lower).
I guess only real fanatics hear the difference

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The NeoGeo would be the same, but faster.
natively running with 59,18 Hz, you would run at 101,38% on 60.00Hz.
that would make the game a little faster and the sound pitch a little higher.
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But... R-Type for example is a example for this being pretty bad.
On a normal PC-VGA-Card, you would have something like 800 x 600 @ 56Hz, which pretty good hits R-Types 55Hz.
However on Soft-15kHz or the ArcadeVGA, it will run at 401 x 256 @ 53Hz, which makes R-Type run with ~96,36% which you most likely will hear (although its not that bad as it sounds).